How to calculate percent difference
Percent difference is used to compare two values when neither value serves as an official reference standard or starting point. Because the order of entry does not matter, the formula normalizes the absolute difference by dividing by the average of the two numbers.
The percent difference formula
Step-by-step example:
- Find the absolute difference: |120 − 150| = 30.
- Find the average of the two numbers: (120 + 150) ÷ 2 = 135.
- Divide the difference by the average: 30 ÷ 135 = 0.2222.
- Multiply by 100 to get the percentage: 0.2222 × 100% = 22.22%.
Percent Difference vs. Percent Change vs. Percent Error
| Measurement Type | When to Use | Mathematical Formula |
|---|---|---|
| Percent Difference | Comparing two equal quantities with no baseline (e.g. comparing two prices) | [|V₁ − V₂| ÷ ((V₁ + V₂) ÷ 2)] × 100% |
| Percent Change | Measuring growth, discount, or decay from old value V₁ to new value V₂ | [(V₂ − V₁) ÷ |V₁|] × 100% |
| Percent Error | Comparing experimental lab results against an accepted scientific standard | [|Experimental − Accepted| ÷ Accepted] × 100% |
Frequently asked questions about percent difference
Why do we divide by the average instead of V1?
Dividing by V1 measures percent change, which produces different answers depending on which number is entered first (120 to 150 is +25%, but 150 to 120 is -20%). Dividing by the average ensures the comparison is symmetric regardless of order.
Can percent difference exceed 100%?
Yes. If one number is significantly larger than the other (for example, comparing 10 and 1,000), the percent difference is (|10 − 1,000| ÷ 505) × 100% = 196.04%. The maximum possible percent difference between any two positive numbers approaches 200% as the smaller number approaches 0.
Created and calculation-tested by Velour Trends · Updated 9 November 2026. Standard arithmetic equations verified. Report a calculation issue.